Prosecutors in the US pushed a judge to set a trial date by spring for Nikolas Cruz in the 2018 Valentine's Day Florida school massacre that killed 17 people.

At a hearing, Assistant State Attorney Jeff Marcus said the case is fairly uncomplicated despite its notoriety and magnitude. He asked Circuit Judge Elizabeth Scherer to schedule the death penalty trial for Cruz in September.

"We are coming up on the anniversary of this incident. Justice requires that this case be resolved as quickly as it can," Marcus said. "It's a pretty straightforward case that does not require years and years to prepare for."

Judge Scherer, however, said she is reluctant to move that quickly, with Cruz's lawyers contending they still have large amounts of evidence to review and dozens of witnesses to interview. Assistant Public Defender Melisa McNeill said there are more than 300 frontline witnesses on the prosecution's list and added that capital cases in Broward County typically take two years or more to get to trial.

"We have to do everything we have to do and depose every witness so that we are effective in our representation of Mr Cruz. There's higher standards of due process," McNeill said.

Scherer instead set another status hearing for February 21 and urged both sides to work as quickly as possible.

"We need to keep moving forward," she said. "I just want to work though this as efficiently as we can."

Cruz, 20, is charged with 17 counts of first-degree murder and 17 counts of attempted murder in the shooting at Marjory Stoneman Douglas High School. His attorneys have said he will plead guilty in exchange for a life prison sentence, but prosecutors have rejected that offer.

Cruz sat silently at the defense table during the hearing, his once unruly hair now closely cropped. He also was wearing oversized glasses.

Separately, Cruz's younger brother Zachary got a green light from a federal judge in his lawsuit accusing the Broward Sheriff's Office of harassment and targeting after he was arrested while skateboarding at Marjory Stoneman Douglas High School shortly after the shooting. Zachary Cruz claims he was treated unfairly, including an unreasonable bail set at US$500,000, was required to wear a restraint vest 24 hours a day and was subjected to sleep deprivation tactics in jail.

The sheriff's office has denied that Zachary Cruz, who attended his brother's hearing Tuesday, was badly treated. Zachary Cruz was eventually released on probation with conditions such as keeping away from the high school.